Virulence determinants, drug resistance and mobile genetic elements of Laribacter hongkongensis: a genome-wide analysis

Background

Laribacter hongkongensis is associated with community-acquired gastroenteritis and traveler's diarrhea. In this study, we performed an in-depth annotation of the genes in its genome related to the various steps in the infective process, drug resistance and mobile genetic elements.

Results

For acid and bile resistance, L. hongkongensis possessed a urease gene cassette, two arc gene clusters and bile salt efflux systems. For intestinal colonization, it possessed a putative adhesin of the autotransporter family homologous to those of diffusely adherent Escherichia coli (E. coli) and enterotoxigenic E. coli. To evade from host defense, it possessed superoxide dismutase and catalases. For lipopolysaccharide biosynthesis, it possessed the same set of genes that encode enzymes for synthesizing lipid A, two Kdo units and heptose units as E. coli, but different genes for its symmetrical acylation pattern, and nine genes for polysaccharide side chains biosynthesis. It contained a number of CDSs that encode putative cell surface acting (RTX toxin and hemolysins) and intracellular cytotoxins (patatin-like proteins) and enzymes for invasion (outer membrane phospholipase A). It contained a broad variety of antibiotic resistance-related genes, including genes related to β-lactam (n = 10) and multidrug efflux (n = 54). It also contained eight prophages, 17 other phage-related CDSs and 26 CDSs for transposases.

Conclusions

The L. hongkongensis genome possessed genes for acid and bile resistance, intestinal mucosa colonization, evasion of host defense and cytotoxicity and invasion. A broad variety of antibiotic resistance or multidrug resistance genes, a high number of prophages, other phage-related CDSs and CDSs for transposases, were also identified.     

POPULATION STRUCTURE OF TWO LABEO SPECIES IN THE HENDRIK VERWOERD DAM AS DETERMINED BY GILL NET SAMPLING

SUMMARY

A series of seven gill nets was used to sample populations of two Labeo species in the Hendrik Verwoerd Dam. Selection curves were computed for these nets and were used to define size and age structure of the two populations; these populations differ markedly, in that the moggel Labeo umbratus has a greater proportion of mature fish, while Labeo capensis (the Orange River Labeo) showed a more normal size and age distribution. Bio-mass curves closely follow the size distribution, while the fecundity of both species is highest in the larger size groups. These data were used to speculate on a fish exploitation strategy for the dam.     

Prevalence of risk factors for cardiovascular disease in Canadians 55 to 74 years of age: results from the Canadian Heart Health Surveys, 1986-1992

BACKGROUND: By 2016, the proportion of Canadians older than 65 years of age will increase to 16%, and there will be an increase in the absolute number of cases of cardiovascular disease in older Canadians. The Canadian Heart Health Surveys database provides information about this population upon which health policy related to cardiovascular disease can be based. This paper presents for the first time population-based data on the risk factors for cardiovascular disease in older Canadians. METHODS: Canadians from all 10 provinces participated in surveys of cardiovascular risk factors; health insurance registries were used as sampling frames. In each province, probability samples of 2200 adults 18 to 74 years old not living in institutions, on reserves or in military camps were asked to participate in interviews and to undergo testing at clinics for major risk factors for cardiovascular disease. RESULTS: A total of 2739 men (response rate 70%) and 2617 women (response rate 66%) aged 55 to 74 years participated in the survey and also provided follow-up clinical measurements at the clinic. Overall, 52% of participants were hypertensive, 26% had isolated systolic hypertension, and 30% had a total blood cholesterol level of 6.2 mmol/L or greater. Rates of current smoking were lower in women than men (17% v. 22%). Overall, 87% of men and 78% of women who were current smokers smoked at least 10 cigarettes per day. Only slightly more than half of participants exercised at least once a week for at least 15 minutes, and almost half had a body mass index of 27 or greater. In only 4% was no major risk factor for cardiovascular disease detected. INTERPRETATION: Significant numbers of older Canadians have one or more major risk factors for cardiovascular disease. Many of these risk factors are amenable to modification.     

The mechanical triggering of bioluminescence in marine dinoflagellates: chemical basis

In both photosynthetic (Pyrodinium bahamense, Gonyaulax polyedra, Pyrocystis Iunula, P. noctiluca, P. fusiformis) and nonphotosynthetic (Noctiluca miliaris) bioluminescent dinoflagellates chemical stimulation can by-pass mechanical stimulation. The effective ions are Ca⁺⁺, K⁺, NH₄⁺ and H⁺. Other chemicals found effective are those implicated in Ca⁺⁺ transport or binding. There are interspecies differences in degrees of mechanical and chemical stimulability. Photoinhibition of mechanical stimulability is the result of two effects, the first a reduction in total bioluminescence potential and the second a decrease in mechanical stimulability resulting experimentally in a decreased rate of light emission. This latter effect can be reversed with Ca⁺⁺ ions. Chemicals which bind Ca⁺⁺ or displace Ca⁺⁺ can mimic the effects of photoinhibition. The chemical inhibition of mechanical stimulability is also reversed by Ca⁺⁺ ions. A scheme is proposed which is consistent for all species examined.     

Differential roles of RIPK1 and RIPK3 in TNF-induced necroptosis and chemotherapeutic agent-induced cell death

Apoptosis is a key mechanism for metazoans to eliminate unwanted cells. Resistance to apoptosis is a hallmark of many cancer cells and a major roadblock to traditional chemotherapy. Recent evidence indicates that inhibition of caspase-dependent apoptosis sensitizes many cancer cells to a form of non-apoptotic cell death termed necroptosis. This has led to widespread interest in exploring necroptosis as an alternative strategy for anti-cancer therapy. Here we show that in human colon cancer tissues, the expression of the essential necroptosis adaptors receptor interacting protein kinase (RIPK)1 and RIPK3 is significantly decreased compared with adjacent normal colon tissues. The expression of RIPK1 and RIPK3 was suppressed by hypoxia, but not by epigenetic DNA modification. To explore the role of necroptosis in chemotherapy-induced cell death, we used inhibitors of RIPK1 or RIPK3 kinase activity, and modulated their expression in colon cancer cell lines using short hairpin RNAs. We found that RIPK1 and RIPK3 were largely dispensable for classical chemotherapy-induced cell death. Caspase inhibitor and/or second mitochondria-derived activator of caspase mimetic, which sensitize cells to RIPK1- and RIPK3-dependent necroptosis downstream of tumor necrosis factor receptor-like death receptors, also did not alter the response of cancer cells to chemotherapeutic agents. In contrast to the RIPKs, we found that cathepsins are partially responsible for doxorubicin or etoposide-induced cell death. Taken together, these results indicate that traditional chemotherapeutic agents are not efficient inducers of necroptosis and that more potent pathway-specific drugs are required to fully harness the power of necroptosis in anti-cancer therapy.Cell death by apoptosis is a natural barrier to cancer development, as it limits uncontrolled proliferation driven by oncogenes.¹ Chemotherapeutic agents that target apoptosis have been successful in anti-cancer therapy. However, cancer cells, especially cancer stem cells, often evolve multiple mechanisms to circumvent growth suppression by apoptosis.² This resistance to apoptosis is a major challenge for many chemotherapeutic agents. Targeting other non-apoptotic cell death pathways is an attractive therapeutic alternative.A growing number of recent studies show that there are distinct genetic programmed cell death modes other than apoptosis.³ Necroptosis is mediated by receptor interacting protein kinase 3 (RIPK3).⁴ In the presence of caspase inhibition and cellular inhibitor of apoptosis proteins (cIAPs) depletion, tumor necrosis factor (TNF) receptor 1 triggers a signaling reaction that culminates in binding of RIPK3 with its upstream activator RIPK1 through the RIP homotypic interaction motif (RHIM).⁴ RIPK1 and RIPK3 phosphorylation stabilizes this complex and promotes its conversion to an amyloid-like filamentous structure termed the necrosome.⁵ Once activated, RIPK3 recruits its substrate mixed lineage kinase domain-like (MLKL).⁶ Phosphorylated MLKL forms oligomers that translocate to intracellular membranes and the plasma membrane, which eventually leads to membrane rupture.^{7, 8, 9, 10}In addition to phosphorylation, RIPK1 and RIPK3 are also tightly regulated by ubiquitination, a process mediated by the E3 ligases cIAP1, cIAP2, and the linear ubiquitin chain assembly complex.¹¹ The ubiquitin chains on RIPK1 act as a scaffold to activate nuclear factor-κB (NF-κB) and mitogen-activated protein kinase pathways and inhibit formation of the necrosome. As such, depletion of cIAP1/2 by second mitochondria-derived activator of caspase (Smac) mimetics or removal of the ubiquitin chains by the de-ubiquitinating enzyme cylindromatosis (CYLD) promotes necroptosis.^{12, 13, 14, 15} In addition, RIPK1 and RIPK3 are cleaved and inactivated by caspase 8.^{16, 17, 18} Mice deficient for caspase 8 or FADD, an essential adaptor protein of caspase 8, suffer from embryonic lethality due to extensive RIPK1- or RIPK3-dependent necroptosis.^{19, 20, 21} Hence, caspase inhibition and IAP depletion are key priming signals for necroptosis.The physiological functions of RIPK1 and RIPK3 have been extensively investigated in infectious and sterile inflammatory diseases.^{4, 22} By contrast, their roles in cancer cells'' response to chemotherapeutics are poorly understood. Here we show that RIPK1 and RIPK3 expression is significantly decreased in human colon cancer tissues, suggesting that suppression of RIPK1 or RIPK3 expression is advantageous for cancer growth. However, the loss of RIPK1 and RIPK3 expression in colon cancer was not due to epigenetic DNA modification. Interestingly, RIPK1 and RIPK3 expression in colon cancer cells is reduced by hypoxia, a hallmark of solid tumor. We found that chemotherapeutic agents did not effectively elicit RIPK1/RIPK3-dependent necroptosis in colon cancer cells. Moreover, caspase inhibition and Smac mimetics, which are potent sensitizers for necroptosis, also did not enhance chemotherapeutic agent-induced cell death. These results show that traditional chemotherapeutic agents are not strong inducers of classical necroptosis in colon cancers and suggest that development of pathway-specific drugs is needed to harness the power of necroptosis in anti-cancer therapy.     

Biogeochemical and Microbial Legacies of Non‐Native Grasses Can Affect Restoration Success

The restoration of disturbed ecosystems is challenging and often unsuccessful, particularly when non‐native plants are abundant. Ecosystem restoration may be hindered by the effects of non‐native plants on soil biogeochemical characteristics and microbial communities that persist even after plants are removed. To examine the importance of soil legacy effects, we used experimental restorations of Florida shrubland habitat that had been degraded by the introduction of non‐native grasses coupled with either mechanical disturbance or pasture conversion. We removed non‐native grasses and inoculated soils with native microbial communities at each degraded site, then examined how habitat structure, soil nitrogen, soil microbial abundances, and native seed germination responded over two years compared to undisturbed native sites. Grass removal treatments effectively restored some aspects of native habitat structure, including decreased exotic grass cover, increased bare ground, and reduced litter cover. Soil fungal abundance was also somewhat restored by grass removals, but soil algal abundance was unaffected. In addition, grass removal and microbial inoculation improved seed germination rates in degraded sites, but these remained quite low compared to native sites. High soil nitrogen persisted throughout the experiment regardless of treatment. Many treatment effects were site‐specific, however, with legacies in the more degraded vegetation type tending to be more difficult to overcome. These results support the need for context‐dependent restoration approaches and suggest that the degree of soil legacy effects may be a good indicator of restoration potential.